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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <h2>js_同步异步</h2>
    <script>
        // 异步
        // console.log(1)
        // setTimeout(() => {
        //     console.log(2)
        // }, 1000)
        // console.log(3)
        // setTimeout(() => {
        //     console.log(4)
        // }, 0)
        // console.log(5)
        //同步
        console.log('a')
        alert('a')
        console.log('b')
    </script>
</body>

</html>